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11.
During its storage or ascent, basaltic magma inevitably interacts with the surrounding rocks. In this study, schist xenoliths incorporated within ascending basalt are examined. Heating of the xenoliths combined with decompression effect of rapid magma uprise led to dehydration melting of hydrous minerals producing hercynitic spinel, melt, sillimanite and FeTi oxides. The melt is rhyolitic, strongly peraluminous (1.77 < A/CNK < 2.35) and corundum normative. It may contain up to 8 wt%FeOt. It occurs between the foliation planes and in the intragranular environment. Dehydration melting of micas in the schist is probably related to combined effects of heating by basaltic magma and decompression due to the rapid rise. Melting of xenoliths was a progressive process at low pressure. To cite this article: H. Bayhan et al., C. R. Geoscience 338 (2006). 相似文献
12.
徐淮地区中生代深部地壳的物质组成及热状态——深源捕虏体证据 总被引：4，自引：0，他引：4
徐淮地区中生代侵入杂岩中含有丰富的深源岩石捕虏体,包括榴辉岩类、单斜辉石岩、角闪岩类和片麻岩类。深源捕虏体的岩相学研究表明,它们经历了早期的榴辉岩相变质和晚期的角闪岩相退化变质,然后被寄主岩浆所捕获。捕虏体中矿物平衡温压估算结果显示,榴辉岩相变质的温压条件为:T=657～992℃,P=1.33～2.78GPa,所反映的地温梯度介于克拉通地温(40mW/m2)和大洋地温(60mW/m2)之间;晚期角闪岩相退变的温压条件为:T=523～878℃,P=0.5～1.02GPa,这与中国东部新生代地温梯度相一致。本区中生代深部地壳主要由一套混杂堆积岩所构成,包括退变榴辉岩、退变石榴辉石岩、角闪岩类和片麻岩类。该区深源捕虏体的P-T演化暗示中生代早期华北地块东部深部地壳和/或岩石圈地幔曾存在一次重要的加厚过程;苏鲁造山带的形成可能是扬子地块沿北西方向俯冲于华北地块之下的产物;中生代郯庐断裂带并不存在巨大左行平移。 相似文献
13.
Three xenoliths erupted as ejecta during recent violent explosion of Stromboli volcano (Aeolian Islands) were investigated in this paper. They consist of high-temperature mineral association (cordierite, hercynite spinels, sillimanite, ±plagioclase, ±mullite, ±corundum) and abundant glass (10–70 vol.%), and may be classified as buchites. The peraluminous composition of the xenoliths, their trace element distribution and REE patterns support their origin from granulite- and amphibolite-facies metapelites of the Calabrian continental crust, which is considered the crystalline basement beneath Stromboli. Buchites have an isotopic composition comparable to that of Stromboli extrusives and significantly different from that of the Calabrian basement.
The glass is generally colourless and has a Si–Al–alkali-rich composition, except for one sample where a Fe–Mg–Ca-rich reddish-brown glass also occurs. These two kinds of glass show complicated textures where patches of reddish-brown glass are often surrounded by plagioclase and/or cordierite or forms streaks and swirls with the colourless glass. Cordierite, plagioclase and oxides have different compositions according to their position in the xenoliths. Ca-rich plagioclase (An72–95), Mg-poor cordierite (Mg-values 47–66) and Al-rich spinels are in the inner portions of the xenoliths and associated with colourless glass; on the contrary, close to the contact with the host lava or associated with coloured glass, cordierite shows higher Mg-values, Ti–Fe-bearing oxides occur and plagioclase is chemically similar to the basalt phenocrysts (An66–71).
The abundant and fresh glass and the idiomorphic shape of the high-temperature minerals suggest that the xenoliths were hold in the basaltic magma, before its extrusion, for a significant time to allow their partial or nearly complete melting and subsequent nucleation and growth of new phases. During this stage, the interaction between the anatectic liquid and the basaltic magma affected the original isotopic composition of the xenoliths and, in some cases, produced glass and mineral phases (cordierite, plagioclase and oxides) with different composition. 相似文献
14.
Highly aluminous xenoliths include kyanite-, corundum- and coesite-bearing eclogites, grospydites and alkremites. These xenoliths are present in different kimberlites of Yakutia but have most often been found in Udachnaya and other pipes of the central Daldyn–Alakitsky region. Kimberlites of this field also contain eclogite-like xenoliths with kyanite and corundum that originate in the lower crust or the lower crust–upper mantle transition zone. Petrographic study shows that two rock groups of different structure and chemistry can be distinguished among kyanite eclogites: fine- to medium-grained with mosaic structure and coarse-grained with cataclastic structure. Eclogites with mosaic structure are characterized by the occurrences of symplectite intergrowths of garnet with kyanite, clinopyroxene and coesite; only in this group do grospydites occur. In cataclastic eclogites, coarse-grained coesite occurs, corresponding in size to other rock-forming minerals. Highly aluminous xenoliths differ from bimineralic eclogites in their high content of Al2O3 and total alkali content. Coesite-bearing varieties are characterized by low MgO content and higher Na/K and Fe2+/Fe3+ ratios, as well as high contents of Na2O. Geochemical peculiarities of kyanite eclogites and other rocks are exhibited by a sloping chondrite-normalized distribution of rare earth elements (REE) in garnets and low Y/Zr ratio, in contrast to bimineralic rocks. Coesite is found in more than 20 kyanite eclogites and grospydites from Udachnaya. Grospydites with coesite from Zagadochnaya pipe are described. Three varieties of coesite in these rocks are distinguished: (a) subhedral grains with size of 1.0–3.0 mm; (b) inclusions in the rock-forming minerals; (c) sub-graphic intergrowths with garnet. The presence and preservation of coesite in eclogites indicate both high pressure of formation (more than 30 kbar) and set a number of constraints on the timing of xenolith cooling during entrainment and transport to the surface. Different ways of formation of the highly aluminous eclogites are discussed. Petrographic observations and geochemistry suggest that some highly aluminous rocks have formed as a result of crystallization of anorthosite rocks in abyssal conditions. δ18O-estimations and other petrologic evidence point out the possible origin of some of these xenoliths as the result of subduction of oceanic crust. Diamondiferous samples have been found in all varieties except alkremites. Usually these eclogites contain cubic or coated diamonds. However, two sample corundum-bearing eclogites with diamonds from the Udachnaya pipe contain octahedra that show evidence of resorption. 相似文献
15.
Nature of diamonds in Yakutian eclogites: views from eclogite tomography and mineral inclusions in diamonds 总被引：1，自引：0，他引：1
Mahesh Anand Lawrence A. Taylor Kula C. Misra William D. Carlson Nikolai V. Sobolev 《Lithos》2004,77(1-4):333-348
We have performed dissections of two diamondiferous eclogites (UX-1 and U33/1) from the Udachnaya kimberlite, Yakutia in order to understand the nature of diamond formation and the relationship between the diamonds, their mineral inclusions, and host eclogite minerals. Diamonds were carefully recovered from each xenolith, based upon high-resolution X-ray tomography images and three-dimensional models. The nature and physical properties of minerals, in direct contact with diamonds, were investigated at the time of diamond extraction. Polished sections of the eclogites were made, containing the mould areas of the diamonds, to further investigate the chemical compositions of the host minerals and the phases that were in contact with diamonds. Major- and minor-element compositions of silicate and sulfide mineral inclusions in diamonds show variations among each other, and from those in the host eclogites. Oxygen isotope compositions of one garnet and five clinopyroxene inclusions in diamonds from another Udachnaya eclogite (U51) span the entire range recorded for eclogite xenoliths from Udachnaya. In addition, the reported compositions of almost all clinopyroxene inclusions in U51 diamonds exhibit positive Eu anomaly. This feature, together with the oxygen isotopic characteristics, is consistent with the well-established hypothesis of subduction origin for Udachnaya eclogite xenoliths. It is intuitive to expect that all eclogite xenoliths in a particular kimberlite should have common heritage, at least with respect to their included diamonds. However, the variation in the composition of multiple inclusions within diamonds, and among diamonds, from the same eclogite indicates the involvement of complex processes in diamond genesis, at least in the eclogite xenoliths from Yakutia that we have studied. 相似文献
16.
鲁东晚白垩世玄武岩及其中幔源包体的岩石学和地球化学研究 总被引：21，自引：3，他引：21
山东胶莱盆地大西庄的王氏群玄武岩属于高钛碱性岩系列,全岩40Ar-39Ar年龄为73.2±0.3Ma,形成于晚白垩世岩石富N2O,Mg#值为63-66,(Ne-Hy-Q)值为6.03-10.05,轻稀土富集,(La/Yb)N比值为11.18-12.56,重稀土有一是程度的分异,富集大离子亲石元素,Tb显著正异常,Zr轻微正异常,具有与大陆板内碱性玄武岩类似的特征。εNd(T)值为7.08-7.55,87Sr/86Sr(T)比值为0.7035-0.7038,反映了玄武岩浆来源于亏损的地幔源区,在上升过程中几乎没有受到地壳物质的混染,原始玄武岩浆由软流圈和新生岩石圈地幔分别部分熔融产生的熔体相混合而形成,起源深度为50-70km。玄武岩含有幔源包体,岩石类型为尖晶石二辉橄榄岩。包体的温压估算结果为T=1010-1140℃,P=20kb。包体的矿物相与平衡温压估算值以及玄武岩浆起源深度估计值表明,胶州地区晚白垩世时岩石圈厚度大约为60-70km,岩石圈地幔具有新生的性质。因此,中国东部岩石圈减薄发生在125-73Ma之间。此后,中国东部进入了统一的以拉张为主的动力学背景之下。 相似文献
17.
Granulite—facies Middle—Lower Crustal Xenoliths from Nueshan Alkali Basalt in Northeastern Anhui Province, China 总被引：1，自引：0，他引：1
Metamorphic xenoliths within the Nushan alkali basalt of northeastern Anhui (NEA),China ,are from the middle-lower crust.They could be divided into two end-members:basic and acid.Interme-diate xenoliths are scarcely found.Basic two-pyroxene granulites(pyriclasites) were formed at 720-810℃ and 7-8kb.Petrological and geochemical studies indicate that the primary magma of the protoliths of basic granulites was derived from the metasomatized upper mantle, while the pa-rental magma of the acid end-member was probably produced by partial melting of the basic rocks. The protoliths of charnockites and grey gneisses represent respectively the early and late crystallization products of the granitic magma.The Nushan granulites are much different in many aspects from the granulites exposed in the northern part of North China ,which implies the inhomogeneity regarding to the early evolution of the North China terranc. 相似文献
18.
Andrew A. Nyblade 《Lithos》1999,48(1-4):81-91
Studies of heat flow from Precambrian terrains have demonstrated three empirical relationships; a temporal relationship between heat flow and tectonic age, a spatial pattern between heat flow and the proximity of Archean cratons, and a temporal relationship between heat flow and the age of lithosphere stabilization. In the first relationship, heat flow is inversely related to tectonic age. The second pattern is characterized by low heat flow from Archean cratons and Proterozoic terrains adjacent to cratonic margins (pericratonic terrains), and higher heat flow from Proterozoic terrains that are more than a few hundred kilometers from a craton. In the third pattern, heat flow decreases as the age of stabilization of the lithosphere increases. A number of interpretations of Precambrian heat flow have been offered to explain one or more of these relationships. The simple cooling of a thermal boundary layer predicts essentially no change in heat flow in terrains older than 1.5 Ga, and therefore does not likely provide a comprehensive framework for the interpretation of Precambrian heat flow. By contrast, two other interpretations, (1) thicker lithosphere beneath Archean terrains than beneath Proterozoic terrains, and (2) greater heat production in Proterozoic crust than in Archean crust, when combined with the special structural configuration of sutures, can both contribute to the spatial and temporal heat flow distributions. Xenolith thermobarometry constraints on lithospheric temperatures, however, limit the contribution of age-dependent crustal heat production, and therefore at least part of the heat flow distributions derive from variations in lithosphere thickness. 相似文献
19.
Spinel lherzolite xenoliths found in Boeun, Korea, have protogranular to porphyroclastic textures and are enclosed in a Miocene alkali basalt. The lithium concentration and isotopic compositions of olivine, clinopyroxene, and orthopyroxene separates from the spinel lherzolite, and whole rocks of the spinel lherzolites and alkali basalt were determined by inductively coupled plasma mass spectrometry (ICP-MS) and multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). The lithium concentrations of the olivines and orthopyroxenes range from 2.2 to 5.0 ppm and from 2.1 to 6.4 ppm, respectively. In contrast, the clinopyroxenes have larger lithium concentrations, from 2.0 to 8.4 ppm, which reflect their preferential lithium enrichment. The lithium isotopic compositions (δ7Li) of olivines (-5.4 to + 3.5‰), orthopyroxenes (-11.4 to -0.1‰), and clinopyroxenes (-14.4 to -4.7‰) range far beyond the average mantle composition of + 4 ± 2‰. The lithium isotopic composition of the host rock, alkali basalt (3.4‰), is within the range of the intraplate and oceanic island basalts. The spinel lherzolites from Boeun exhibits strong elemental and isotopic disequilibria due to the different lithium and lithium isotope diffusion velocities in the olivine, orthopyroxene, and clinopyroxene minerals after eruption and magma cooling. 相似文献
20.
道县虎子岩岩体及其包体的地球化学特征和构造意义 总被引：14，自引：0，他引：14
虎子岩碱性橄榄玄武岩具有与大陆裂谷玄武岩相似的地球化学特征。通过对岩体及其尖晶石二辉橄榄岩包体地球化学特征的研究,揭示了本区地幔在先期亏损的基础上又迭加了一次交代事件,虎子岩基性岩浆是由交代地幔约16％的低程度部分熔融的产物。用辉石温压计估算出,包体矿物的平衡结晶温度为1038—1109℃,压力为22—25×10~8 Pa,推测包体来源深度为72—85km。岩体形成可能是受郯庐断裂南延带拉张(裂谷)阶段控制。 相似文献